Nuclear reactors in general and pressurized water nuclear reactors in particular include components, such as the reactor containment vessel, steam generators and the pressurizer which are made of low alloy high strength constructional steel lined with a layer of stainless steel, and connected by one or more connecting tubes to one or more austenitic stainless steel pipes constituting parts of the primary circuit of the reactor, for example.
Steam generators of pressurized water nuclear reactors include a water box having a hemispherical wall constituting the lower part of the steam generator in which are two connecting tubes welded to two pipes of the primary circuit of the reactor.
The connecting tubes of the steam generator, which are made of constructional steel lined with stainless steel, must be butt-welded to an austenitic stainless steel pipe.
It is therefore necessary to make a heterogeneous welded joint between the connecting tube and the pipe, the heterogeneous weld being effected by depositing a filler metal into a groove formed between the connecting tube and the pipe or between the connecting tube and an intermediate austenitic stainless steel connector.
Before effecting the heterogeneous weld between the connecting tube and the pipe or the intermediate connector, it is necessary to deposit a thick layer of stainless steel or nickel alloy onto an end part of the connecting tube constituting one surface delimiting the groove into which the filler metal is deposited during welding.
A process of this kind, which necessitates preparation of the areas of the parts to be jointed after they are machined, is difficult and necessitates a relatively long execution time.
The welded joint is effected by juxtaposing weld beads in the form of successive layers superposed in the direction of the thickness of the parts, this direction being substantially perpendicular to the longitudinal direction of the welded joint. Each of the layers which occupies all of the width of the groove between the two parts, in a direction perpendicular both to the longitudinal direction and to the direction of the thickness of the parts, is made up of a possibly large number of juxtaposed weld beads, depending on the average width of the groove.
If the TIG process is used, each of the weld beads is obtained by melting a filler wire by means of an electrode fed with a particular current at a particular voltage. The filler metal wire which is fed at a fixed speed into the weld area is melted by the electric arc formed between the electrode and the parts to be welded in the groove.
It is also possible to use other welding processes such as the covered electrode process.
Obtaining successive layers of filler metal having a substantially constant thickness combined with very high quality and a good consistency of the filler metal requires totally accurate control of welding conditions during the deposition of each of the weld beads.
Prior art heterogeneous welding jointing processes are therefore complex and their execution times can be very long.